What is added to 5,9,17,27 to be in proportion
( 5 + x ) / ( 9 + x ) = ( 17 + x ) / ( 27 + x )
( 5 + x ) * ( 27 + x ) = ( 17 + x ) * ( 9 + x )
x ^ 2 + 32 x + 135 = x ^ 2 + 26 x + 153
32 x - 26 x = 153 - 135
6 x = 18
x = 3
( 5 + x ) / ( 9 + x ) = ( 17 + x ) / ( 27 + x )
( 5 + 3 ) / ( 9 + 3 ) = ( 17 + 3 ) / ( 27 + 3 )
8 / 12 = 20 / 30
4 * 2 / 4 * 3 = 10 * 2 / 10 * 3
2 / 3 = 2 / 3